1. Field of the Invention
The present invention relates to an intermediate transferring belt adapted to an intermediate transferring body of full-color copiers and printers, a process for producing the intermediate transferring belt, an image forming apparatus, and image forming process that utilize the intermediate transferring belt respectively.
2. Description of the Related Art
In forming full color images by means of an image forming apparatus such as a copier and printer, such a process is conventionally conducted that the respective mono-color toner images are separately formed on a photoconductor, the respective mono-color toner images are duplicately transferred on an intermediate transferring belt, then the respective mono-color toner images on the intermediate transferring belt are entirely transferred at one time to form a multi-color image by means of an electrostatic force. In forming the multi-color images on such an intermediate transferring body in the electrostatic process, a higher resistivity layer is effectively provided on the substrate of the transferring body for achieve higher image quality. In other words, the control of resistivity is a key technology for electrostatic transferring process. Conventionally, the necessary level of electrostatic force is derived by applying a voltage of 500 to 2000 V, i.e. above 15 MV/m of electric field.
On the other hand, energy saving is demanded also for image forming apparatuses in light of environmental issues in recent years. As for the effective countermeasures of the energy saving, for example, eco-starting apparatuses and low-energy fixing processes have been progressing.
Previously, the higher image quality due to higher resistivity layer of the intermediate transferring belt have been attained through complex-layer construction by providing the higher resistivity layer as the surface layer on the substrate layer.
However, the intermediate transferring belts of the prior art suffer from the delamination between the higher resistivity layer and the substrate layer. That is, when the bonding between the higher resistivity layer and the substrate layer is not sufficient, the higher resistivity layer partly comes to detach and raise from the substrate surface after repeated usages, resulting in non-conductive parts in the higher resistivity layer and occurrences of image nonuniformity.
In order to solve such a problem, an image forming apparatus is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 08-160654, in which a surface layer is produced by dipping step after forming a substrate of an intermediate transferring body. Further, JP-A No. 2003-165127 discloses an intermediate transferring body in terms of the specific gravity of conductive material. In the intermediate transferring body, some thermoplastic resins and thermosetting resins are utilized in addition to polyimide.
JP-A No. 11-109761 discloses a technology concerning an intermediate transferring belt, process for producing the same, and image forming apparatus, in which plural types of carbon with different electric conductivities are included in a film and the carbon is distributed in a gradient along the film thickness.
In such a construction, the surface resistivity is different between the front side and back side, since the plural types of carbon with different conductivities distribute in a gradient along the film thickness, consequently, the intermediate transferring belt may suppress image nonuniformity.
In addition, polyimide resin is a valuable material with respect to strength, thermal resistance, and triboelectrification property. The electrophotographic intermediate transferring belt having a mono-layer construction, formed from polyimide resin and carbon black dispersed therein, have demonstrate superior properties compared with other materials such as plastics.
However, two types of carbon powder with different conductivities and two dispersing steps are necessary to produce the proposed intermediate transferring belt. Moreover, the possibility could not be completely removed that the carbon with different conductivities may flocculate together at local sites around the belt surface.
Further, the resistivity of belts is difficult to be controlled into desired ranges so as to be utilized for various electrographic processes, since the resistivity of belt is often determined depending on material factors such as the resistivity of carbon itself, added amount and the like.
With respect to energy saving, conventional intermediate transferring belts are not satisfactory as explained earlier, since electrostatic force should be derived by applying a voltage of as high as 500 to 2000 V, in other expression about up to 30 MV/m of transferring voltage.
In order to lower the applied voltage, there exist two ways in general. One way is to lower the resistance of the belt, another way is to reduce the applied energy. However, when the resistance of the belt is lowered, the charge required for transferring is not stabilized on the surface or inside the belt and is likely to migrate, as a result the transferring efficiency is unsatisfactory and the transferring is inferior.
On the other hand, when the applied energy is reduced, the absolute amount of charge required for transferring is reduced at the toner layer, the transferring is unsuccessful due to the lowered energy at the toner layer and the insufficient energy in the electric field.